Most cancer cells elicit an immune response that is evident by the presence of immune cell infiltrates and inflammation. This response, however, is not strong enough to overcome the cancer cell's defence strategies. Approaches taken to promote an immune response against cancer cells include stimulating a subject's immune cells, in particular, their dendritic cells, to recognise cancer-cell specific antigens in vitro and then injecting these back into the subject.
The molecular and cellular interaction between the immune system and a tumour is complex and it is only relatively recent that the importance of normal cells, tissues and chemokine/cytokine responses in this interaction has been recognised. Blood vessels, connective tissue, stroma and extra-cellular matrix all play a part in supporting tumour growth and the inflammatory environment supplied by the immune system further stimulates growth.
The lack of understanding of the complex interactions between tumours and the immune system has hindered the development of cancer immunotherapy. Approaches involving using purified tumour antigens and more complex mixtures of tumour antigens have failed to stimulate adequate immune responses against tumours. The reasons for this are unknown, but may include the genetic instability of tumours and the ability of tumours to evade the immune system by presenting a “normal” appearance or releasing inhibitors. Tumours can respond to an immune response by reducing the amount of targeted antigens, by masking antigens from the immune system or by expressing mutated versions of antigens that are no longer recognised. Such defensive strategies undermine the immune system, making it difficult to maintain an effective immune response at the level required to halt tumour growth and cause regression.
Mesenchymal stem cells (MSCs) are post-natal, multipotent, adult stem cells. Mesenchymal stem cells (MSCs) are present in many tissues in the body and play an important role in tissue repair and regeneration. For therapeutic purposes MSCs are commonly harvested from bone marrow, cord blood and adipose tissue. In many circumstances the cells are expanded by tissue culture prior to use. Adipose tissue has the unique advantage as a source of MSCs that such large numbers of MSCs are present in the tissue that for many applications the cells do not need to be expanded by tissue culture.
MSCs are currently being investigated as therapeutic agents for the treatment of various diseases including osteoarthritis, MS, rheumatoid arthritis, renal disease and heart disease.